Lean, high conductivity, relaxation-resistant beryllium-nickel-copper alloys

ABSTRACT

A higher order beryllium-nickel-copper alloy a process for making the same, and an article of manufacture comprising the alloy, the alloy being represented by the formula (0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+[0.06-1% Zr) and/or (0.06-1% Ti)], the balance copper, where the sum of % Zr and % Ti is generally within a range of 0.06% and 1%, the alloy being characterized by improved electrical conductivity, bend formability and stress relaxation resistance without sacrificing strength.

This is a division of prior application Ser. No. 08/965,878, filed Nov.7, 1997, now U.S. Pat. No. 5,993,574, which in turn is a division ofprior application Ser. No. 08/738,880, filed Oct. 28, 1996, now U.S.Pat. No. 6,001,196.

FILED OF THE INVENTION

The present invention relates generally to alloys and more particularlyto a lean alloy of beryllium-nickel-copper having high conductivity andstress relaxation resistance.

BACKGROUND OF THE INVENTION

Beryllium-copper alloys are notable for their superior combination ofhigh conductivity, formability, strength and resistance to corrosion.For these seasons, they are considered particularly suited to theconstruction of electronic connectors for automobiles and lead framesfor semi-conductor chips.

In conventional beryllium-copper alloys, cobalt has been used as anadditive to improve strength, In this connection, nickel has also beenadded, alternatively or concurrently with cobalt, with the added benefitof increasing the alloy's conductivity. In an attempt to lower cost,decreased beryllium content has been considered. However, the resultshave been concurrent loss of strength, formability, stress relaxationresistance, and in some cases conductivity.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a highperformance beryllium-nickel-copper alloy with superior stressrelaxation resistance without sacrificing formability, conductivity orstrength.

Another object of the present invention is to provide a high performancealloy with superior electrical conductivity.

A further object of the present invention is to provide a lower costberyllium-nickel-copper alloy with enhanced mechanical properties.

Still another object of the present invention is to provide a method ofproducing beryllium-nickel-copper alloys which improves bend formabilitywithout sacrificing other desirable alloy characteristics.

Yet another object of the present invention is to provide simple,efficient and economical production of novel high performance alloysusing conventional methods.

A further object of the present invention is to provide a lean alloy ofberyllium-nickel-copper while enhancing its properties.

Yet a further object of the present invention is to improve performanceof electronic connectors.

Still another object of the present invention is to enhance performanceof semi-conductor lead frames.

Another object of the present invention is to enable direct recycling oftin-plated scrap upon processing beryllium-nickel-copper alloys withoutthe expense of chemical detinning and while retaining a high degree ofhot workability.

According to one aspect of the present invention is a higher orderberyllium-nickel-copper alloy represent by the formula (0.15-0.5%Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+(0.06-1% Zr), the balance copper,characterized by improved electrical conductivity, bend formability andstress relaxation resistance without sacrificing strength.

In accordance with another aspect of the present invention is a higherorder beryllium-nickel-copper alloy represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+(0.06-1% Ti), the balancecopper, characterized by improved electrical conductivity, bendformability and stress realization resistance without sacrificingstrength.

In accordance with a further aspect of the present invention is a higherorder beryllium-nickel-copper alloy represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+(0.06-1% Zr)+(0.06-1% Ti),the balance copper, where the sum of % Zr and % Ti is generally within arange of 0.06% and 1%, the alloy being characterized by improvedelectrical conductivity, bend formability and stress relaxationresistance without sacrificing strength.

In accordance with still another aspect of the present invention is amethod of producing a lean beryllium-nickel-copper alloy with tin andzirconium and/or titanium additions represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+[(0.06-1% Zr) and/or(0.06-1% Ti)], the balance copper, where the sum of %Zr and %Ti isgenerally within a range of 0.06% and 1%, the method comprising thesteps of: (i) melting a composition represented by the formula, (ii)casting the melt into billets, (iii) hot rolling the billets into strip,(iv) cold rolling the strip to a selected ready-to-finish thickness, (v)final solution annealing the cold rolled strip at a temperaturegenerally within a range of 1550° F. and 1700° F. followed by rapidquenching, (vi) cold working the annealed strip generally within a rangeof 0% and 90% to final thickness, and (vii) final age hardening the coldworked strip at a temperature generally within a range of 750° F. and950° F. for a time generally within a range of 1 and 16 hrs.

In accordance with still a further aspect of the present invention is amethod of producing a lean beryllium-nickel-copper alloy with tin andzirconium and/or titanium additions represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+[(0.06-1% Zr) and/or(0.06-1% Ti)], the balance copper, where the sum of %Zr and %Ti isgenerally within a range of 0.06% and 1%, the method comprising thesteps of: (i) melting a composition represented by the formula, (ii)casting the melt into billets, (iii) hot rolling the billets into strip,(iv) intermediate annealing the hot rolled strip to improve formability,(v) cold rolling the strip to a selected ready-to-finish thickness, (vi)final solution annealing the cold rolled strip at a temperaturegenerally within a range of 1550° F. and 1700° F. followed by rapidquenching, (vii) cold working the annealed strip a generally within arange of 0% and 90% to final thickness, and (viii) final gage hardeningthe cold worked strip at a temperature generally within a range of 750°F. and 950° F. for a time generally within a range of 1 and 16 hrs.

In accordance with yet another aspect of the present invention is amethod of producing a lean beryllium-nickel-copper alloy with tin andzirconium and/or titanium additions represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+[(0.06-1% Zr) and/or(0.06-1% Ti)], the balance copper, where the sum of % Zr and % Ti isgenerally within a range of 0.06% and 1%, the method comprising thesteps of: (i) melting a composition represented by the formula, (ii)casting the melt into billets, (iii) hot rolling the billets into strip,(iv) cold rolling the hot rolled strip to an intermediate thickness, (v)intermediate annealing the cold rolled strip, (vi) cold rolling theannealed strip to a selected ready -to-finish thickness, (vii) finalsolution annealing the cold rolled strip to improve bend formability,(viii) cold working the annealed strip generally within a range of 0%and 90% to final thickness, and (ix) final age hardening the cold workedstrip at a temperature generally within a range of 750° F. and 950° F.for a time generally within a range of 1 and 16 hrs.

Although the present invention is shown and described in connection withberyllium-nickel-copper alloys, it may be adapted for improvingcharacteristics of other precipitation hardenable materials such asaluminum-based alloys and other copper or nickel-based alloys.

Still other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to the discovery of a unique combinationof constituents which, when added to beryllium-nickel-copper alloys, notonly reduces the proportion of beryllium necessary to maintain thealloys' performance, but also improves properties of the material.

Such materials have been found particularly desirable for use in leadframes and electronic connectors for high technology applications.Exemplary lead frames are shown, for example, in U.S. Pat. Nos.5,437,096 and 5,525,836, which issued on Aug. 1, 1995 and Jun. 11, 1996,respectively, the disclosures of which are hereby incorporated byreference in their entirety. Sample electronic connectors are set forthin U.S. Pat. No. 5,037,311, which issued on Aug. 6, 1991 and in the"Connector Engineering Design Guide"--Material Selection in the Designof Spring Contacts and Interconnection, by Brush Wellman Inc.--TechnicalStaff, July, 1995the disclosures of which are hereby incorporated byreference in their entirety.

To illustrate, circuit integrity in electronic connectors often dependsupon maintenance of a minimum contact normal force over the life of amated connector, During operation of the connector at elevatedtemperatures, a phenomenon known as "stress relaxation" may occur.Stress relaxation, by one definition, is a thermally-activated loss innormal force at a constant spring deflection over time at an elevatedtemperature. It has been found that connectors which require a specifiedminimum normal force for electrical continuity must necessarily be overdesigned with respect to the normal force at room temperature, in orderto compensate for any expected time-dependent stress loss throughrelaxation at usual operating temperatures.

An undesirable side effect of "overdesigning" is an increase ininsertion force. Alloys with a high stress relaxation resistance notonly allow the use of a lower insertion force but also enable thinnerstrip and/or smaller spring beams to be used, thereby reducing cost.And, this is done without sacrificing contact performance.

Stress realization is normally measured on tapered cantilever beamspecimens, deflected in a fixture to impart an initial stress that is apredetermined fraction of the 0.2% offset yield strength at roomtemperature of the strip being tested. Stress relaxation is measured asthe "% remaining" initial stress after exposure for various times (aslong as about 1000 hrs. and, in some cases, up to about 10,000 hrs.) ata selected temperature.

Stress relaxation resistance typically falls within three categoriesamong conductive spring alloys, depending on the strengthening mechanismat work in the alloy. The lowest grade relaxation resistance is found incopper alloys strengthened only by solid solution and cold work (e.g.,C26000 brass and C51000 phosphor bronze). Next are precipitation(nucleation and growth) hardened copper alloys (e.g., C17200C17510,C17500, C17410, and C7025) whose heat treated strength generation offersignificantly higher stress relaxation resistance. Further increase inrelaxation resistance has been found in copper alloys strengthened byspinodal decomposition (or spinodal alloys) in response to heattreatment (e.g., C72900and 4 wt % Ti--Cu).

Another significant parameter is bend formability. Bend formability isthe minimum punch radius without cracking "R" divided by the stripthickness "T" when bend by a male punch in a 90 degree V-block underconditions of "plane strain" (specimen width to thickness ratio muchgreater than about 8:1).

The foregoing discussion is provided for purposes of illustration and isnot intended to limit the intended environment. The remaining aspects ofconnectors and lead frames are known by those skilled in the art andfurther description is believed unnecessary for illustration of thepresent invention.

In accordance with one aspect of the present invention is a higher orderberyllium-nickel-copper alloy represented by the formula (0.15-0.5%Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+(0.06-1% Zr), the balance copper. Suchalloys are advantageous in having improved electrical conductivity, bendformability and stress relaxation resistance, but without sacrificingstrength.

According to another aspect of the present invention is a higher orderberyllium-nickel-copper alloy represented by the formula (0.15-0.5%Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+(0.06-1% Ti), the blance copper. Thisalloy is similarly characterized by improved electrical conductivity,bend formability and stress relaxation resistance. Again, strength isnot sacrificed.

Alternatively, an alloy is provided represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+(0.06-1% Zr)+(0.06-1% Ti),the balance copper. With this alloy, the sum of % Zr and % Ti isgenerally within a range of 0.0% and 1%. As before, electricalconductivity, bend formability and stress relaxation resistance areimproved, and strength is maintained.

Generally speaking, the foregoing combinations and constituent rangeshave consistently improved properties of beryllium-nickel-copper alloysfor purpose of high performance applications. Such alloys not onlyprovide strength comparable to conventional alloys, but also improvedformability,. conductivity and stress relaxation resistance overcompetitive alloys such as C7025, C7026 and other heat treatedcopper-based alloys for strip products. It is noted, the percent of eachconstituent is preferably weight based, as will be appreciated by thoseskilled in the art.

Referring now to Table I, there are provided specific, illustrativecompositions and methods according to the present invention. Eachcomposition was first induction melted in air in a commercial-scalefurnace and semi-continuously cast into strip billets bout 7 inchesthick nominal. Conventional manufacturing processes were then employedto convert the cast billets to strip, as follows.

In accordance with one aspect of the present invention, leanberyllium-nickel-copper alloys with tin and zirconium and/or titaniumadditions are produced. The alloys are represented by the formula(0.15-0.5% Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+[(0.06-1% Zr) and/or(0.06-1% Ti)], the balance copper, where the sum of %Zr and %Ti isgenerally within a range of 0.06% and 1%. The method comprises the stepsof (i) melting a composition represented by the formula, (ii) castingthe melt into billets, (iii) hot rolling the billets into strip, (iv)cold rolling the strip to a selected ready-to-finish thickness, (v)final solution annealing the cold rolled strip at a temperaturegenerally within a range of 1550° F. and 1700° F. followed by rapidquenching, (vi) cold working the annealed strip generally within a rangeof 0% and 90% to final thickness, and (vii) final age hardening the coldworked strip at a temperature generally within a range of 750° F. and950° F. for a time generally within arrange of 1 and 16 hrs.

                                      TABLE I                                     __________________________________________________________________________    ALLOYS, PROCESSING AND PROPERTIES                                                                    Inter-                     Elect                                                                             Good                                                                             Bad                                     Final                                                                             med.    Cold                                                                             Final           Cond.                                                                             Way                                                                              Way                                                                              Strs.             Heat                                                                             Be  Ni  Sn  Zr  Other                                                                             Ann.*                                                                             Ann.                                                                              Wrk                                                                              Age Hard.                                                                          0.2% YS                                                                            UTS                                                                              Elong                                                                            %   Bend                                                                             Bend                                                                             Rem               Num.                                                                             (wt %)                                                                            (wt %)                                                                            (wt %)                                                                            (wt %)                                                                            (wt %)                                                                            (F.)                                                                              (F.)                                                                              (%)                                                                              (F.)/# hr                                                                          (ksi)                                                                              (ksi)                                                                            (%)                                                                              IACS                                                                              (R/t)                                                                            (R/t)                                                                            (%)*              __________________________________________________________________________    1  0.12                                                                              0.48                                                                              0.120                                                                             --  --  No  1550                                                                              20  850/16                                                                            45.6  65.5                                                                            15.7                                                                             --  -- -- --                                           1550                                                                               0 950/5                                                                              48.2  64.3                                                                            14.8                                                                             61.9                                                                              0  0  --                                           1600                                                                              20 750/5                                                                              70.7  86.2                                                                            12.0                                                                             58.3                                                                              0.38                                                                             0.31                                            1780                                                                              20 850/5                                                                              80.7  91.4                                                                             6.0                                                                             66.0                                                                              0.50                                                                             0.31                                                                             --                2  0.19                                                                              0.50                                                                              0.125                                                                             0.081                                                                             --  No  1650                                                                              20 750/5                                                                              84.2 102.2                                                                            15.0                                                                             59.1                                                                              0.38                                                                             0.25                                            1650                                                                              20 950/5                                                                              74.6  86.7                                                                            12.0                                                                             61.4                                                                              0.75                                                                             0.38                                                                             --                                           1700                                                                               0 750/5                                                                              64.3  96.7                                                                            20.0                                                                             50.5                                                                              0.30                                                                             0  --                                           1700                                                                               0 950/5                                                                              62.4  88.6                                                                            18.0                                                                             62.0                                                                              -- -- --                3  0.18                                                                              0.76                                                                              0.180                                                                             0.069                                                                             --  No  1600                                                                              20 750/5                                                                              92.4 111.0                                                                            14.0                                                                             57.1                                                                              0.75                                                                             0.25                                                                             --                                           1650                                                                               0 750/5                                                                              67.2 100.7                                                                            20.0                                                                             54.4                                                                              0.60                                                                             0  --                                           1650                                                                              20 750/5                                                                              93.1 112.0                                                                            14.0                                                                             57.2                                                                              0.88                                                                             0.38                                                                             --                                           1700                                                                               0 750/5                                                                              71.2 103.9                                                                            20.0                                                                             54.3                                                                              0.70                                                                             0  --                                           1650                                                                               0 950/5                                                                              70.5  94.4                                                                            20.0                                                                             61.5                                                                              -- -- 83                                           1650                                                                              20 950/5                                                                              82.6  93.7                                                                            11.0                                                                             63.1                                                                              1.00                                                                             0.63                                                                             --                4  0.22                                                                              0.43                                                                              0.22                                                                              0.13                                                                              --  No  1600                                                                              20 750/5                                                                              80.8  99.8                                                                            16.0                                                                             54.6                                                                              0.38                                                                             0.25                                                                             --                                           1650                                                                               0 750/5                                                                              61.3  93.0                                                                            22.0                                                                             55.0                                                                              0.10                                                                             0  --                                           1650                                                                              20 750/5                                                                              83.0 101.8                                                                            15.0                                                                             54.4                                                                              0.38                                                                             0.25                                                                             --                                           1700                                                                               0 750/5                                                                              60.9  93.9                                                                            22.0                                                                             53.2                                                                              0  0  --                                           1650                                                                               0 950/5                                                                              56.4  83.4                                                                            18.0                                                                             56.2                                                                              0.22                                                                             0.43                                                                             --                5A 0.22                                                                              0.74                                                                              --  0.146                                                                             --  No  1700                                                                              20 750/5                                                                              105.6                                                                              121.3                                                                             8.9                                                                             54.3                                                                              0.75                                                                             0.38                                                                              85.              5C 0.22                                                                              0.74                                                                              --  --  --  No  1700                                                                              20 750/5                                                                              107.4                                                                              121.1                                                                             7.0                                                                             54.4                                                                              0.88                                                                             0.38                                                                              76.              6                                                                             6A 0.23                                                                              0.73                                                                              0.107                                                                             0.128                                                                             --  No  1700                                                                              20 750/5                                                                              100.8                                                                              117.8                                                                            12.8                                                                             53.5                                                                              0.50                                                                             0.38                                                                              93.              6C 0.23                                                                              0.73                                                                              --  --  --  No  1700                                                                              20 950/5                                                                              82.7  95.2                                                                             9.8                                                                             59.8                                                                              1.25                                                                             0.62                                                                              86.                                     No  1700                                                                              20 750/5                                                                              100.8                                                                              116.7                                                                             8.0                                                                             53.0                                                                              0.75                                                                             0.50                                                                              85.                                     No  1700                                                                              20 950/5                                                                              85.4  99.4                                                                             8.6                                                                             57.1                                                                              0.75                                                                             0.5                                                                               88.              7  0.24                                                                              0.74                                                                              0.130                                                                             0.160                                                                             --  No  1650                                                                               0 700/8                                                                              39.9  69.7                                                                            21.8                                                                             --  -- -- --                                                  750/8                                                                              53.7  83.8                                                                            20.1                                                                             --  -- -- --                                                  850/1                                                                              86.2 104.5                                                                            13.5                                                                             --  -- -- --                                                  850/2                                                                              90.0 104.9                                                                            12.6                                                                             --  -- --                                                     850/8                                                                              91.5 103.9                                                                            11.4                                                                             --  -- -- --                                                   850/16                                                                            91.2 102.8                                                                            10.6                                                                             --  -- -- --                                                  950/1                                                                              74.1  98.0                                                                            16.6                                                                             --  -- -- --                                                  950/8                                                                              64.5  87.1                                                                            15.6                                                                             --  -- -- --                8  0.24                                                                              1.04                                                                              0.245                                                                             0.117                                                                             --  No  1550                                                                               0 750/5                                                                              71.7  98.5                                                                            -- --  0  0  --                                           1550                                                                               0 950/5                                                                              78.3  96.2                                                                            16.0                                                                             53.9                                                                              0.40                                                                             0.40                                                                             --                                           1650                                                                               0 950/5                                                                              82.5 103.1                                                                            16.0                                                                             53.8                                                                              -- --                   9                                                                             9B 0.22                                                                              1.19                                                                              --  0.113                                                                             --  No  1700                                                                              20 750/5                                                                              114.0                                                                              129.3                                                                            11.1                                                                             50.8                                                                              0.75                                                                             0.50                                                                             --                   0.22                                                                              1.19                                                                              --  --  --  No  1700                                                                              20 750/5                                                                              113.8                                                                              129.7                                                                            11.8                                                                             50.7                                                                              0.75                                                                             0.88                                                                             --                10                                                                            1B 0.24                                                                              1.18                                                                              0.128                                                                             0.179                                                                             --  No  1700                                                                              20 750/5                                                                              115.5                                                                              130.0                                                                            10.9                                                                             49.8                                                                              1.25                                                                             0.63                                                                             --                1C 0.24                                                                              1.18                                                                              0.128                                                                             --  --  No  1700                                                                              20 750/5                                                                              115.5                                                                              130.3                                                                            11.3                                                                             49.6                                                                              1.25                                                                             0.75                                                                             --                11 0.28                                                                              0.69                                                                              0.27                                                                              0.160                                                                             --  No  1600                                                                              20 750/5                                                                              96.5 115.7                                                                            14.0                                                                             51.4                                                                              0.63                                                                             0.38                                                                             --                                           1650                                                                               0 750/5                                                                              75.6 108.5                                                                            16.0                                                                             49.2                                                                              0.30                                                                             0  --                                           1650                                                                              20 750/5                                                                              98.4 116.9                                                                            14.0                                                                             50.9                                                                              0.63                                                                             0.38                                                                             --                                           1700                                                                               0 750/5                                                                              75.6 110.0                                                                            18.0                                                                             49.2                                                                              0.30                                                                             0  --                                           1650                                                                               0 950/5                                                                              66.0  94.7                                                                            22.0                                                                             53.7                                                                              0.90                                                                             0.40                                                                             --                                           1650                                                                              20 950/5                                                                              81.8  94.6                                                                            -- 55.0                                                                              0.63                                                                             0.25                                                                             --                12 0.24                                                                              0.79                                                                              0.179                                                                             0.151                                                                             --  No  1550                                                                              10 900/5                                                                              86.3 103.8                                                                            15.1                                                                             --  -- -- --                                           1600                                                                              10 850/5                                                                              88.1 109.5                                                                            18.0                                                                             55.3                                                                              0.34                                                                             0  --                                           1650                                                                              20 850/5                                                                              96.5 113.3                                                                            13.0                                                                             55.2                                                                              0.86                                                                             0  --                                       HR  1550                                                                               0 900/5                                                                              77.3  97.3                                                                            15.0                                                                             55.6                                                                              -- -- --                                       &   1600                                                                              10 850/5                                                                              90.3 111.3                                                                            18.0                                                                             56.4                                                                              0.45                                                                             0  --                                       WQ  1650                                                                              20 850/5                                                                              100.9                                                                              114.5                                                                            11.0                                                                             56.1                                                                              0.65                                                                             0  --                13 0.26                                                                              0.75                                                                              0.208                                                                             0.123                                                                             --  1550                                                                              1550                                                                              10 900/5                                                                              81.7 100.1                                                                            11.1                                                                             --  -- -- --                                       (0.075                                                                            1600                                                                              10 850/5                                                                              80.5 102.8                                                                            18.0                                                                             54.0                                                                              0  0  --                                       in.)                                                                              1650                                                                              20 850/5                                                                              89.5 106.4                                                                            13.0                                                                             53.8                                                                              0  0  --                14 0.26                                                                              0.72                                                                              0.201                                                                             0.130                                                                             --  1600                                                                              1550                                                                              10 850/5                                                                              82.0 103.5                                                                            21.0                                                                             --  0  0  --                                       (0.300                                                                            1600                                                                              10 850/5                                                                              83.4 107.0                                                                            17.0                                                                             52.3                                                                              0.11                                                                             0.22                                                                             --                                       in.)                                                                              1650                                                                              20 850/5                                                                              91.7 109.3                                                                            13.0                                                                             52.7                                                                              0.13                                                                             0.25                                                                             --                                       1700                                                                              1650                                                                               0 950/5                                                                              77.7 103.8                                                                            20.0                                                                             61.9                                                                              -- --  83.                                     (0.300                                                                            1550                                                                              30 850/5                                                                              91.6 105.4                                                                            13.6                                                                             --  0.57                                                                             0.57                                                                             --                                       in) 1550                                                                              40 850/5                                                                              95.2 106.7                                                                            12.1                                                                             --  0.50                                                                             0.75                                                                             --                                           1550                                                                              50 850/5                                                                              96.3 107.0                                                                            11.7                                                                             --  0.50                                                                             0.60                                                                             --                                           1550                                                                              60 850/5                                                                              98.5 108.0                                                                             8.7                                                                             --  0  0.75                                                                             --                                           1550                                                                              80 850/5                                                                              93.0 103.0                                                                             9.2                                                                             --  -- -- --                                           1550                                                                              90 850/5                                                                              86.0  92.6                                                                             5.6                                                                             --  -- -- --                15 0.27                                                                              1.05                                                                              0.118                                                                             0.132                                                                             --  No  1650                                                                               0 850/1                                                                              99.6 115.0                                                                            12.9                                                                             --  -- -- --                                           1650                                                                               0 850/2                                                                              99.4 114.4                                                                            12.2                                                                             --  -- -- --                                           1650                                                                               0 850/8                                                                              100.8                                                                              112.2                                                                            10.3                                                                             --  -- -- --                                           1650                                                                               0  850/16                                                                            101.4                                                                              111.6                                                                             9.8                                                                             --  -- -- --                                           1600                                                                              20 750/5                                                                              103.0                                                                              120.1                                                                            17.0                                                                             55.1                                                                              0.75                                                                             0.38                                                                             --                                           1650                                                                              20 750/5                                                                              106.5                                                                              124.2                                                                            15.0                                                                             53.8                                                                              1.13                                                                             0.63                                                                             --                                           1700                                                                               0 750/5                                                                              87.1 120.3                                                                            19.0                                                                             50.9                                                                              1.40                                                                             0  --                                           1700                                                                              20 750/5                                                                              81.0 109.8                                                                            15.0                                                                             59.3                                                                              -- -- --                16 0.31                                                                              0.50                                                                              0.130                                                                             0.078                                                                             --  No  1600                                                                              20 750/5                                                                              90.8 110.9                                                                            12.0                                                                             53.0                                                                              0.50                                                                             0.13                                                                             --                                           1650                                                                              20 750/5                                                                              69.3 104.5                                                                            20.0                                                                             51.1                                                                              0.20                                                                             0  --                                           1700                                                                               0 750/5                                                                              68.6 102.2                                                                            20.0                                                                             50.5                                                                              0  0  --                                           1700                                                                              20 750/5                                                                              56.7  87.5                                                                            20.0                                                                             54.2                                                                              -- -- --                17 0.32                                                                              0.73                                                                              0.128                                                                             0.115                                                                             --  No  1700                                                                              20 750/5                                                                              110.4                                                                              127.2                                                                            12.1                                                                             47.2                                                                              0.75                                                                             0.50                                                                             --                18 0.33                                                                              0.77                                                                              --  0.125                                                                             --  No  1700                                                                              20 750/5                                                                              111.4                                                                              128.7                                                                            11.5                                                                             50.0                                                                              0.75                                                                             0.50                                                                             --                19 0.32                                                                              0.89                                                                              0.13                                                                              --  --  No  1550                                                                               0 850/5                                                                              63.4  87.6                                                                            20.4                                                                             --  -- -- --                                           1550                                                                              20 850/5                                                                              90.2 103.6                                                                            13.9                                                                             50.7                                                                              -- -- --                                           1650                                                                              10 850/5                                                                              93.1 115.7                                                                            15.6                                                                             49.5                                                                              -- -- --                                           1650                                                                              20 750/5                                                                              105.5                                                                              123.0                                                                            13.9                                                                             --  -- -- --                                           1650                                                                              20 950/5                                                                              84.3  99.5                                                                            11.3                                                                             --  -- -- --                20                                                                            20A                                                                              0.33                                                                              1.22                                                                              --  0.152                                                                             --  No  1700                                                                              20 750/5                                                                              119.4                                                                              135.6                                                                            10.5                                                                             48.9                                                                              0.75                                                                             0.50                                                                              85.              20C                                                                              0.33                                                                              1.22                                                                              --  --  --  No  1700                                                                              20 750/5                                                                              116.7                                                                              133.3                                                                            11.8                                                                             49.2                                                                              0.88                                                                             0.88                                                                              76.              21                                                                            21A                                                                              0.32                                                                              1.20                                                                              0.141                                                                             0.158                                                                             --  No  1700                                                                              20 750/5                                                                              119.7                                                                              135.5                                                                            11.6                                                                             47.4                                                                              0.75                                                                             0.63                                                                             --                21C                                                                              0.32                                                                              1.20                                                                              0.141                                                                             --  --  No  1700                                                                              20 750/5                                                                              111.1                                                                              127.0                                                                            13.5                                                                             48.3                                                                              0.75                                                                             0.50                                                                              78.              22 0.28                                                                              0.71                                                                              --  --  --  No  1700                                                                              60 750/5                                                                              96.8 111.3                                                                            14.3                                                                             55.9                                                                              -- --  77.              23 0.26                                                                              0.75                                                                              --  --  0.46                                                                              No  1700                                                                              60 750/5                                                                              76.6  84.7                                                                             7.8                                                                             30.9                                                                              -- --  97.                                 Ti                                                         24 0.32                                                                              0.77                                                                              --  --  1.00                                                                              No  1700                                                                              60 750/5                                                                              105.5                                                                              111.7                                                                             8.1                                                                             25.7                                                                              -- --  97.                                 Ti                                                         25 0.27                                                                              0.75                                                                              --  0.47                                                                              --  No  1700                                                                              60 750/5                                                                              86.2  99.2                                                                            11.8                                                                             52.3                                                                              -- --  96.              26 0.32                                                                              0.78                                                                              --  1.12                                                                              --  No  1600                                                                              20 850/5                                                                              70.4  85.5                                                                            12.0                                                                             54.5                                                                              -- -- --                __________________________________________________________________________     (*Note: "No" Intermediate Anneal = Air Cool at Hot Roll + CR + Final          Anneal                                                                        (**Note % Stress Remaining after 1000 hr at 175 C. and Initial Stress of      75% of 0.2% YS)                                                          

According to another aspect of the present invention is a method ofproducing alloys represented by the formula (0.15-0.5% Be)+(0.40-1.25%Ni)+(0-0.25% Sn)+[(0.06-1% Zr) and/or (0.06-1% Ti)], the balance copper,Again, the sum of %Zr and %Ti is generally within a range of 0.06% and1%. The method, however, comprises the steps of: (i) induction melting acomposition represented by the formula, (ii) casting the induction meltinto billets, (iii) hot rolling the billets into strip, (iv)intermediate annealing the hot rolled strip to improve bend formability,(v) cold rolling the annealed strip to a selected ready-to-finishthickness, (vi) final solution annealing the cold rolled strip at atemperature generally within a range of 1550° F. and 1700° F. followedby rapid quenching, (vii) cold working the final annealed stripgenerally within a range of 0% and 90% to final thickness, and (viii)final age hardening the cold worked strip at a temperature generallywithin a range of 750° F. and 950° F. for a time generally within arange of 1 and 16 hrs.

In accordance with a further aspect of the present invention is a methodof producing a lean beryllium-nickel-copper alloy with tin and zirconiumand/or titanium additions represented by the formula (0.15-0.5%Be)+(0.40-1.25% Ni)+(0-0.25% Sn)+[(0.06-1% Zr) and/or (0.06-1% Ti)] isgenerally within a range of 0.06% and 1%. by this method, a compositionrepresented by the formula is first melted, e.g. by induction, and castinto billets. Next, the billets are hot rolled into strip, and the stripcold-rolled to intermediate thickness. Intermediate annealing isperformed on the cold rolled strip to improve bend formability. Theannealed strip is then cold rolled to a selected ready-to-finishthickness. Thereafter, the cold rolled strip is final solution annealedat a temperature generally within a range of 1550° F. and 1700° F.followed by rapid quenching, and cold worked generally within a range of0% and 90% to final thickness. Final age hardening is performed on thecold worked strip at a temperature generally within a range of 750° F.and 950° F. for a time generally within a range of 1 and 16 hrs.

More particularly, the billets are hot rolled to strip preferably about0.3 in. to about 0.8 in. thick nominal. Also, the strip is air cooled(or, alternatively, water quenched) from a hot finishing temperature toroom temperature after being rolled into coils on a hot mill, the coilsmay also be intermediate annealed a hot rolled thickness. The hot rolledcoils are then preferably milled to remove any oxide scale, and coldrolled to ready-to-finish thickness on the order of about 0.020 in, Theready-to-finish thickness, by one definition, is the predeterminedthickness (intended for application of a final solution annealing step)sufficient to allow a selected amount of additional cold work to a finalthickness.

Optionally, second intermediate anneal and cleaning steps are performedpart way through the cold rolling process between the milled thicknessand ready-to-finish thickness. The second annealing step may beinserted, alternatively, after hot rolling.

At ready-to-finish thickness, the coils are solution annealed at atemperature generally within a range of 1550° F. to 1700° F., as shownin Table I, followed by rapid quenching and chemical cleaning. Coils arethen cold rolled 0% to about 60%, 80% or up to about 90% to finalthickness. Final age hardening is preferably performed at a temperaturegenerally within a range of 750° F. and 950° F. for about 1 hr. to about16 hrs., preferably about 5 hrs., at such temperature.

Finally, selected strip samples are evaluated for tensile properties(0.2% offset yield strength, ultimate tensile strength and elongation),bend formability, electrical conductivity and stress relaxationresistance at about 175° C. for up to about 1000 hrs., at an initialstress fo about 75% of the 0.2% offset yield strength.

Although the present invention is shown and described in connection withthe production of strip, analogous processes may be practiced to producethe alloy in wire or rid form, within the spirit and scope of thepresent invention.

As shown in Table I, a yield strength lower than a desirable minimum,i.e., about 65 ksi for a low strength electronic connector for leadframe, were found in lean beryllium-nickel-copper alloys withcompositions generally within a range of (0.12-0.31% Be)+(0.48-0.745%Ni), the balance copper, with optional Sn and/or Zr. This was also truewhere the alloy was processed with apparent combinations of insufficientannealing temperatures, e.g., about 1550° F. for the leanest Becontents, insufficient cold work, e.g., 0 to about 20%, and/or final agehardening at conditions considered to be either (i) under aged, e.g., attemperature that are considered too low such as about 700° F., or fortimes believed too short to reach maximum possible aged strength, e.g.,about 1 hr.; or (ii) over aged at, e.g., about 950° F., or for timessuch as about 8-16 hrs. so long that precipitates responsible for agehardening become coarse, resulting in irrecoverable loss of strength.

It has been found that yield strengths generally within a range from65-93 ksi are achieved the composition range (0.12-0.19) wt % Be,(0.48-0.76) wt % Ni, balance Cu and optional Sn and/or Zr, processed byannealing at about 1600° F.--about 1700° F., cold rolling up to about20% and age hardenign generally between 750° F. and 950° F. for about 5hrs.

Yield strengths between about 65 and about 107 ksi are achieved inalloys in the range (0.22-0.34 ) wt % Be, (0.43-0.89) wt % Ni, thebalance Cu and optional Sn and/or Zr, by the following process:annealing at a temperature generally within a range of 1550° F. and1700° F., cold rolling up to about 90% to and age hardening at atemperature generally within a range of 750° F.-950° F. at least about 5hrs. is used for the lower aging temperatures of this range.

From about 65-120ksi, yield strengths were achieved in alloys in thecomposition range (0.22-0.33) wt % be, (1.04-1.22) wt % Ni, balance Cuand optional Sn and/or Zr, processed by annealing at a temperaturebetween about 1550° F. and about 1700° F., cold rolling up to about 20%and age hardening between about 750° F.-950° F. for about 1 to about 16hrs. Again, at least 5 hrs. is desired at aging temperatures low in thisrange.

Overall, the preferred lean beryllium-nickel-copper alloys, inaccordance with various aspects fo the present invention, were found tolie within the following nominal composition ranges: (0.1-0.4%Be)+(0.4-1.25% Ni), the balance Cu, with additions of (0.1-0.25% Snnominal) and (0.15% Zr nominal).

Alloys which contain the full stated constituent ranges and areprocessed in accordance with the present invention, it has been found,meet or exceed the desired property combinations for representativestrip tempers as follows:

(a) 65-85 ksi 0.2% offset yield strength with bend formability of0.25-0.05 R/t in both "good way" and "bad way" bend directions(applicable to low strength electronic connectors and lead frames);

(b) 85-105 ksi yield strength with bend formability of 0.5-1.0 R/t inboth bend directions (applicable to moderate strength electronicconnectors and selected lead frames);

(c) 105-120 ksi yield strength with 1.0-1.5 R/t bend formability in bothbend directions (applicable primarily to high strength electronicconnectors);

(d) a minimum of 45-50% IACS electrical conductivity at all strengthlevels; and

(e) a minimum of 85-90% remaining stress in stress relaxation test for1,000 hrs. at 175° C. and an initial stress of 75% of the 0.2% offsetyield strength.

Each composition and process combinations which met target yieldstrengths for each of the selected strip tempers also met target bendformability levels for the tempers. As Ni content approached about 1.22wt %, the risk that electrical conductivity would fall below about 50 %IACS increased. However, the alloys surveyed met the target minimum ofabout 45 %IACS.

These lean beryllium-nickel-copper alloys also hot rolledsatisfactorily, Additions of up to about 0.25 wt. % Sn, with or withoutZr, had no apparent effect. Further, up to about 0.25 wt % Sn wastolerated at acceptable electrical conductivity of finish age hardenedstrip where no more than about 1.04 wt %, up to about 0.13 wt % Sn wastolerated in terms of acceptable finished strip electrical conductivity.In general, Sn additions seemed to have no impact upon yield strength,bend formability or stress relaxation resistance.

Finally, the addition of about 0.12-0.15 wt % Zr improved stressrelation resistance at about 175° C. in the lean alloys to a levelconsistent with at least the lower desired target, e.g., about85remaining stress, established for the strip tempers selected. Evengreater improvement in stress relaxation resistance was achieved, abovethe upper desired target, e.g., about 90% remaining stress, withadditions of about 0.47% Zr or about 1.12% Zr as well as with additionof about 0.46% Ti or about 1% Ti. Absent Zr or Ti, this competitiveadvantage was not achieved. Also, the addition of up to about 0.15 wt %Zr was found to be of no consequence to yield strength or electricalconductivity, and had either no impact on, or was slightly beneficialto, bend formability. At about 1.12% Zr, some loss in strength andelectrical conductivity was apparent, although within selected targetranges, addition of about 0.46% Ti or about 1% Ti significantly reducedelectrical conductivity and had a variable impact on strength.

Intermediate anneals at hot rolled thickness or at any thickness betweenhot rolled and ready-to-finish thickness improved bend formability atall strength levels of the finished strip. In addition, final agehardening at a temperature generally within a range of 750° F. and 850°F. provided greater resistance to stress relaxation than final agehardening at 950° F.

By traditional processing, the property combinations achieved aresuperior to competitive copper alloys such as C7025, C7026 and like heattreated copper-based alloys, In addition, these alloy provided improvedelectrical conductivity and "bad way" bend formability withoutsacrificing strength, as compared to C17410 lean beryllium-cobalt-copperalloys.

Adding nominal 0.15% Zr to lean Be-Ni-Cu alloys yielded improvements instress relaxation resistance at 175° C. so substantial that theirrelaxation behavior exceeded that of alloy C17410. It has also beendiscovered that the addition of up to about 0.25% Sn can be made to leanBe-Ni-Cu alloys without sacrificing hot rollability of cast billets andelectrical conductivity for Ni contents up to nominal 1%. Above about 1%Ni, nominal 0.15% Sn was tolerated somewhat better in terms ofelectrical conductivity.

Turning now to the economic benefits, three factors are believed tocontribute to the relatively lower cost of these alloys, first is theircapacity to develop useful properties at reduced beryllium contentsrelative to those of prior beryllium-cobalt-copper alloys, Second,nickel rather than higher cost cobalt has been found workable as analternative charge material. Finally, the combination of constituents ofthe present invention provides an apparently high tolerance of impuritysolid solution alloying elements, such as tin. This enables directmelting in Sn-plated scrap without the added expense of scrap detinningoperation. Tin contamination in C17410 has been found to degradeelectrical conductivity and make hot rolling more difficult.

A sum of % Zr and %Ti generally within a range of 0.06% and 1% has beenfound relatively important to operation and effectiveness of the presentinvention. For instance, below this range no measurable improvement instress relaxation has been achieved. Above the range, age hardeningresponse and/or electrical conductivity were found to be adverselyaffected.

Although the present invention is shown and described in connection withberyllium-nickel-copper alloys, it may be adapted for improvingdesirable characteristics of other precipitation hardenable materialssuch as aluminum-based alloys as well as copper or nickel-base alloys.Tin, according to at least one aspect of the present invention, may beexcluded from the composition, giving consideration to the purpose forwhich the present invention is intended.

Other lean beryllium-copper alloys having enhanced stress relaxationresistance, at somewhat higher nickel content, have also been achieved.Alloys of this type are described, for example, in a co-pending U.S.patent application, filed on the same date herewith by John C. Harknessand Shelley J. Wolf, entitled "Lean, High Conductivity,Relaxation-Resistant Beryllium-Copper Alloys", the disclosure of whichis hereby incorporated by reference in its entirety.

Various impurities, e.g., lead, iron, cobalt, chromium, silicon,aluminum, zinc, magnesium and silver are believed inherent in alloys ofpresent invention, as will be appreciated by those skilled in the art.

The present invention advantageously eliminates the need for cobalt andreduces the amount of beryllium necessary, permitting cost-effectivemass production of lead frames and connectors, while enhancing theperformance characteristics of the alloys for electronic applications.

The alloy compositions illustrate increased resistance to stressrelaxation associated with the addition of these specified amounts ofzirconium and/or titanium. They also provide the benefit of tin-platedscrap consumption up to selected maximum tin levels to be cast intobillet form, without the added expense of a scrap detinning step, yetretaining commercially desirable electrical conductivity and a highdegree of hot workability.

Various modifications and alterations to the present invention may beappreciated based on a review of this disclosure. These changes andadditions are intended to be within the scope and spirit of thisinvention as defined by the following claims.

What is claimed:
 1. A method of producing a higher orderberyllium-nickel-copper alloy consisting essentially of about 0.15 to0.5% Be, about 0.40 to 1.25% Ni, about 0 to 0.25% Sn and about 0.06 to1% Zr, Ti or both, the balance being copper, wherein the alloy has beenage hardened without substantial overaging and exhibits a stressrelaxation resistance after 100 hours at 175° F. of about 86 to 97%, ayield strength of at least 65 ksi, an ultimate tensile strength of about87 to 135 ksi, and an electrical conductivity of about 50 to 63% IACS,the method comprising final age hardening a previously cold worked alloyat a temperature generally within a range of 750 and 950 ° F. for about1 to 16 hours without substantial overaging, the previously cold workedalloy being obtained by,(i) cast a melt of the ingredients of the alloy,(ii) hot rolling the casting so formed, (iii) cold rolling the castingto a selected ready-to-finish thickness, (iv) final solution annealingthe alloy at a temperature generally within a range of 1550 to 1700° F.followed by rapid quenching, and (v) cold working the annealed alloy togenerally within a range of 0 and 90% to final thickness.
 2. The methodof claim 1, wherein the alloy contains about 0.06 to 1% Zr.
 3. Themethod of claim 1, wherein the alloy contains about 0.06 to 1% Ti. 4.The method of claim 1, wherein the alloy is age hardened at about 750 to850 ° F.
 5. The method of claim 4, wherein the alloy is substantiallypeak aged.
 6. The method of claim 5, wherein the alloy contains about0.4 to 0.9% Ni.
 7. The method of claim 5, wherein the alloy containsabout 0.15% Zr.
 8. The method of claim 1, wherein prior to finalsolution annealing, the alloy is intermediate annealed to improve bendformability.
 9. The method of claim 8, wherein prior to intermediateannealing, the alloy is cold rolled to a selected intermediatethickness.
 10. A method of producing a higher orderberyllium-nickel-copper alloy consisting essentially of about 0.15 to0.5% Be, about 0.40 to 1.25% Ni, about 0 to 0.25% Sn and about 0.06 to1% Zr, Ti or both, the balance being copper, wherein the alloy has beenage hardened without substantial overaging and exhibits a stressrelaxation resistance after 1000 hours at 175° F. of about 86 to 97%, ayield strength of at least 65 ksi, an ultimate tensile strength of about87 to 135 ksi, and an electrical conductivity of about 50 to 64%IACS,the method comprising cold working a final solution annealed alloy togenerally within a range of 0 and 90% to a final thickness and thenfinal age hardening the previously cold worked alloy at a temperaturegenerally within a range of 750 and 950° F. for about 1 to 16 hourswithout substantial overaging, the final solution annealed alloy beingobtained by:(i) casting a melt of the ingredients of the alloy, (ii) hotrolling the casting so formed, (iii) cold rolling the casting to aselected ready-to-finish thickness, and (iv) final solution annealingthe alloy at a temperature generally within a range of 1550 to 1700° F.followed by rapid quenching.
 11. The method of claim 10, wherein thealloy contains about 0.06 to 1% Zr.
 12. The method of claim 10, whereinthe alloy contains about 0.06 to 1% Ti.
 13. The method of claim 10,wherein the alloy is age hardened at abut 750 to 850° F.
 14. The methodof claim 13, wherein the alloy is substantially peak aged.
 15. Themethod of claim 14, wherein the alloy contains about 0.04 to 0.9% Ni.16. The method of claim 14, wherein the alloy contains about 0.15% Zr.17. The method of claim 10, wherein prior to final solution annealing,the alloy is intermediate annealed to improve bend formability.
 18. Themethod of claim 17, wherein prior to intermediate annealing, the alloyis cold rolled to a selected intermediate thickness.